A Lenses

Posse96 · 03-13-2019, 02:45 PM

Good Day All,

This is one of the moments in life when you just completely lose any thought; a brain fart. I'm probably asking a question most will think is obvious, but seriously, my brain is just not functioning this week.

I have a K-3 Limited. One of my lenses is a Sigma 20mm 1: 1.8 that I use for star shots and landscape. My cam was flashing F-- today and I realized the lens was not set to "A" It got me thinking, and that can just be a bad thing some days because I just overthink. Obviously, as a Sigma lens, I have to put it on the A setting, which prohibits from using the varied f-stops on the lens. Knowing that, is there any disadvantage to utlizing A settings on varied lenses vs using lenses (more often than not, Pentax lenses) that allow you to pic specific settings. In short, is the A (automatic) setting as reliable as the standard setting?

I've never really found discussions on this and was wondering. I do like Pentax, I only have Pentax cams, but have found not all Pentax lenses are great. I've had some under-perform compared to some Sigmas and others which often requires you use the A setting.

Thanks

**BigMackCam** · 03-13-2019, 03:08 PM - **2 Likes**

Hello and welcome

Any K-mount lens, whether Pentax, Sigma, Tamron or otherwise, with a dedicated aperture ring and "A" setting on it allows you to set the aperture from the camera's control wheel by setting the ring to the "A" position. Then, from within any of the P, Sv, Tv, Av, TAv, M and B modes, you select the aperture of the lens using the control wheel on the camera. For lenses without a dedicated aperture ring (e.g. Pentax DA lenses), they operate as those with a ring set to the "A" position.

I don't know what Pentax and Sigma lenses you've been using. Generally, I would say most modern Pentax lenses are great. Older models vary, but are mostly OK-to-excellent. Sigma lenses are, in my experience, much more variable in performance depending on whether they're primes, zooms, and the era in which they were developed and released. Generally, I prefer Pentax lenses. But there are exceptions, such as the DA*16-50, where the Sigma equivalent - in this case, the 17-50 f/2.8 HSM - is arguably better optically.

The latest Sigma lenses can be very good indeed, but those that are compatible with Pentax K-mount sometimes have inconsistent or unreliable auto-focusing, as Sigma reverse-engineered Pentax AF operation when designing its lenses, rather than paying for a licence to use the official specification

Adam · 03-13-2019, 03:13 PM - **1 Like**

The aperture ring is obsolete (on DSLRs). Unless you are reverse mounting the lens or something like that, then simply leave the aperture ring in the "A" setting and then set the aperture using the e-dial (or automatically).

pschlute · 03-13-2019, 03:56 PM - **1 Like**

If you have a lens with aperture ring and "A" setting then use the "A" setting. Taking the ring out of "A" severely restricts what exposure modes can be used with a modern DSLR. Basically you are stuck with Manual and need to use stop down metering. In any other mode such as Av , the camera will only use wide open aperture irrespective what you set on the lens.

MarkJerling · 03-13-2019, 04:14 PM - **2 Likes**

Originally posted by Posse96

Obviously, as a Sigma lens, I have to put it on the A setting, which prohibits from using the varied f-stops on the lens.

I'd like to address only this sentence of yours.

Originally posted by Posse96

Obviously, as a Sigma lens, I have to put it on the A setting,....

The A setting is available on many lenses, not only Sigma. It simply means that you can use your camera to set the lens aperture, you don't have to set it on the lens.

Originally posted by Posse96

....which prohibits from using the varied f-stops on the lens.

The camera is still capable of using all the varied f-stop settings. Nothing is prohibited, provided you ensure you use your camera in one of the modes where changing the F-stop value is possible.

stevebrot · 03-13-2019, 05:02 PM

Originally posted by Posse96

In short, is the A (automatic) setting as reliable as the standard setting?

Good question. Much depends on the aperture ring implementation as well as the aperture actuator implementation for a particular lens. If both are well-calibrated and robust, the two methods of setting aperture are fully equivalent in terms of accuracy and precision for the aperture settings supported by both*. Notice the emphasis on the word "If". The camera does not check the accuracy or precision of its aperture controller against the actual behavior of the lens**. Likewise, even if a lens aperture ring was properly calibrated at the factory, there is potential for falling out of spec with age and wear. It might be good to note that even wide-open, many (most? all?) prime lenses fail to deliver a true f/1.4, f/2, or whatever at infinity and get progressively "slower" at closer planes of focus. Similar problems occur with zooms at different focal lengths. These failings apply to both ways of setting the aperture opening.

Does all this leave us in the weeds? Probably only if we are using an external meter or are a little a**l-retentive about rightness of settings. TTL metering provides compensation for attenuation due to focal length and/or extension for close focus. Also in our favor is that differences from the expected aperture diameter are usually quite minimal at all but the narrowest settings. If you have doubts and your lens has an aperture ring, you can do comparison shots of an evenly-lit blank wall for a given f-number.

Steve

* Most aperture rings support at most 1/2 stop increments and often not for all stops. In a similar vein, if the camera is set to 1/3 stop increments and the aperture ring has no settings that correspond to a 1/3 stop, there is no point for comparison.

** Probably not a bad idea for a future feature. After all, we fine-tune AF, why not aperture control?

**dms** · 03-13-2019, 07:37 PM - **3 Likes**

Originally posted by Adam

The aperture ring is obsolete (on DSLRs). Unless you are reverse mounting the lens or something like that, then simply leave the aperture ring in the "A" setting and then set the aperture using the e-dial (or automatically).

I respectfully disagree. It is sometimes very useful to set the exposure in M mode, and then depending on the subject/lighting very quickly change the aperture setting on the lens to adjust the exposure (and thus almost instantly get the shot). It requires you to have a reasonable sense of exposure/estimating the change needed, and comfort using the aperture ring--but these are likely normal for many of us--especially coming from the (slide) film era.

Last edited by dms; 03-13-2019 at 07:52 PM. Reason: fix typo

Paul the Sunman · 03-14-2019, 03:11 AM - **2 Likes**

Originally posted by Adam

The aperture ring is obsolete (on DSLRs).

The most recent Pentax lens release (HD FA 35mm f/2) has an aperture ring.

**clackers** · 03-14-2019, 07:53 AM - **1 Like**

Originally posted by Paul the Sunman

The most recent Pentax lens release (HD FA 35mm f/2) has an aperture ring.

Very mischievous of you, Paul!

Racer X 69 · 03-14-2019, 10:33 AM - **2 Likes**

Bring back the aperture ring, and the A setting.

I shoot nearly 100% in manual mode. I use the camera to meter the scene, except for night time and low light shots, which I usually guess at.

Most of my lenses are manual lenses, and I have been leaning towards the ones with the A setting. I like the A setting, because I can set the aperture using the thumbwheel on the camera, and see what aperture I am at in the viewfinder.

I prefer having the aperture ring so when I am using a bellows or extension tubes, or shooting with the lens reversed, i still have control over the aperture.

I know, there is an adapter that adapts K mount lenses to Nikon, that has an aperture ring to manually control the aperture, and if one removes the optics it has to adjust for infinity focus when used as designed, it facilitates using lenses without aperture rings.

*sigh*

Guess I just am nostalgic about the aperture ring.

stevebrot · 03-14-2019, 11:00 AM - **1 Like**

Originally posted by Racer X 69

Guess I just am nostalgic about the aperture ring.

Me too. I prefer the lens controls to be on the lens and the camera controls to be on the camera. With a non-crippled mount, this works very nicely, even on a "modern" camera (example: Pentax MZ-S) and if such a mount were on the K-3 successor, I would be the happiest of clams with the option of both e-dials and aperture ring.

Steve

**Mikesul** · 03-14-2019, 12:22 PM - **2 Likes**

There may be a trend in the industry. The recent, highly rated and very expensive Sony GM primes (24 1.4, 85 1.4 and 135 1.4) have aperture rings and, of course, the A position.

**WPRESTO** · 03-14-2019, 01:04 PM

I doubt that a manually set aperture set via an aperture ring is necessarily more accurate than one set using an "A" setting and letting the camera set the aperture, that is, if you set f5.6 on an aperture ring, it's unlikely it is more precisely and exactly f5.6 than the aperture the camera sets when using the "A" setting and selecting f5.6 via the camera. And if the lens is set to anything other than infinity, chances are the aperture won't be exactly f5.6 regardless of whether the lens is unit focusing or internal focusing. AND ALSO, the human eye can barely detect a 1/3 f-stop change, so if either the ring or the camera sets f5.6 within plus or minus about 20%, it's nearly certain that you could not tell the difference.

Posse96 · 03-14-2019, 09:22 PM - **1 Like**

Good Evening,

I thank you all, fantastic feedback. Of course, I wake up in the middle of the night, starting to realize what you all conveyed. I have to shake my head at myself as I work in DNA Forensics and Biometrics. I can build a $5 Mln ABIS (Automated Biometric ID System), and yet, there are times when, as I noted, the obvious just escapes me. As most pointed out, I awake in bed; "you idiot, you're using the cam dial to set the settings" and it just went from there.

I agree with those who highlighted variations in lenses and quality. I will say, I've been very pleased with the Pentax SMC 15mm f/4.0 DA ED AL Limited Wide Angle. Yet was so so with the Pentax DA 55-300mm f/405.8 ED lens. My goal now is to find a good landscape lens. I've been making the move back to prime lenses and find I wasn't satisfied with a large range zoom like the 55-300mm as photo clarity and quality didn't see that great.

I accept all recommendations on suggestions for a solid landscape lens.

Again, thanks everyone. I really appreciate the patience of a guy who, as I say; train went into the ravine (my explanation of a lost thought).

Racer X 69 · 03-15-2019, 07:06 AM

Originally posted by Posse96

Good Evening,

I thank you all, fantastic feedback. Of course, I wake up in the middle of the night, starting to realize what you all conveyed. I have to shake my head at myself as I work in DNA Forensics and Biometrics. I can build a $5 Mln ABIS (Automated Biometric ID System), and yet, there are times when, as I noted, the obvious just escapes me. As most pointed out, I awake in bed; "you idiot, you're using the cam dial to set the settings" and it just went from there.

I agree with those who highlighted variations in lenses and quality. I will say, I've been very pleased with the Pentax SMC 15mm f/4.0 DA ED AL Limited Wide Angle. Yet was so so with the Pentax DA 55-300mm f/405.8 ED lens. My goal now is to find a good landscape lens. I've been making the move back to prime lenses and find I wasn't satisfied with a large range zoom like the 55-300mm as photo clarity and quality didn't see that great.

I accept all recommendations on suggestions for a solid landscape lens.

Again, thanks everyone. I really appreciate the patience of a guy who, as I say; train went into the ravine (my explanation of a lost thought).

The Pentax A28mm (three different versions) should work well.

I have the Sigma 28mm f2.8 Mini Wide and have used it quite a bit since I picked it up. There is an A version of this lens I would like to try.

03-13-2019, 02:45 PM	#1
Posse96 New Member Join Date: Feb 2019 Location: San Francisco Posts: 6	A Lenses Good Day All, This is one of the moments in life when you just completely lose any thought; a brain fart. I'm probably asking a question most will think is obvious, but seriously, my brain is just not functioning this week. I have a K-3 Limited. One of my lenses is a Sigma 20mm 1: 1.8 that I use for star shots and landscape. My cam was flashing F-- today and I realized the lens was not set to "A" It got me thinking, and that can just be a bad thing some days because I just overthink. Obviously, as a Sigma lens, I have to put it on the A setting, which prohibits from using the varied f-stops on the lens. Knowing that, is there any disadvantage to utlizing A settings on varied lenses vs using lenses (more often than not, Pentax lenses) that allow you to pic specific settings. In short, is the A (automatic) setting as reliable as the standard setting? I've never really found discussions on this and was wondering. I do like Pentax, I only have Pentax cams, but have found not all Pentax lenses are great. I've had some under-perform compared to some Sigmas and others which often requires you use the A setting. Thanks

03-13-2019, 03:08 PM - 2 Likes	#2
BigMackCam Digitiser of Film Join Date: Mar 2010 Location: North East of England Posts: 20,673	Hello and welcome Any K-mount lens, whether Pentax, Sigma, Tamron or otherwise, with a dedicated aperture ring and "A" setting on it allows you to set the aperture from the camera's control wheel by setting the ring to the "A" position. Then, from within any of the P, Sv, Tv, Av, TAv, M and B modes, you select the aperture of the lens using the control wheel on the camera. For lenses without a dedicated aperture ring (e.g. Pentax DA lenses), they operate as those with a ring set to the "A" position. I don't know what Pentax and Sigma lenses you've been using. Generally, I would say most modern Pentax lenses are great. Older models vary, but are mostly OK-to-excellent. Sigma lenses are, in my experience, much more variable in performance depending on whether they're primes, zooms, and the era in which they were developed and released. Generally, I prefer Pentax lenses. But there are exceptions, such as the DA16-50, where the Sigma equivalent - in this case, the 17-50 f/2.8 HSM - is arguably better optically. The latest Sigma lenses can be very good indeed, but those that are compatible with Pentax K-mount sometimes have inconsistent or unreliable auto-focusing, as Sigma reverse-engineered Pentax AF operation when designing its lenses, rather than paying for a licence to use the official specification Last edited by BigMackCam; 03-13-2019 at 03:15 PM.*

03-13-2019, 03:13 PM - 1 Like	#3
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,595	The aperture ring is obsolete (on DSLRs). Unless you are reverse mounting the lens or something like that, then simply leave the aperture ring in the "A" setting and then set the aperture using the e-dial (or automatically). Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

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03-13-2019, 03:56 PM - 1 Like	#4
pschlute Moderator Loyal Site Supporter Join Date: Mar 2007 Location: Surrey, UK Photos: Gallery Posts: 8,202	If you have a lens with aperture ring and "A" setting then use the "A" setting. Taking the ring out of "A" severely restricts what exposure modes can be used with a modern DSLR. Basically you are stuck with Manual and need to use stop down metering. In any other mode such as Av , the camera will only use wide open aperture irrespective what you set on the lens.

03-13-2019, 04:14 PM - 2 Likes	#5
MarkJerling Moderator Site Supporter Join Date: May 2012 Location: Wairarapa, New Zealand Photos: Gallery \| Albums Posts: 20,406	Originally posted by Posse96 Obviously, as a Sigma lens, I have to put it on the A setting, which prohibits from using the varied f-stops on the lens. I'd like to address only this sentence of yours. Originally posted by Posse96 Obviously, as a Sigma lens, I have to put it on the A setting,.... The A setting is available on many lenses, not only Sigma. It simply means that you can use your camera to set the lens aperture, you don't have to set it on the lens. Originally posted by Posse96 ....which prohibits from using the varied f-stops on the lens. The camera is still capable of using all the varied f-stop settings. Nothing is prohibited, provided you ensure you use your camera in one of the modes where changing the F-stop value is possible.

03-13-2019, 05:02 PM	#6
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Posse96 In short, is the A (automatic) setting as reliable as the standard setting? Good question. Much depends on the aperture ring implementation as well as the aperture actuator implementation for a particular lens. If both are well-calibrated and robust, the two methods of setting aperture are fully equivalent in terms of accuracy and precision for the aperture settings supported by both. Notice the emphasis on the word "If". The camera does not check the accuracy or precision of its aperture controller against the actual behavior of the lens. Likewise, even if a lens aperture ring was properly calibrated at the factory, there is potential for falling out of spec with age and wear. It might be good to note that even wide-open, many (most? all?) prime lenses fail to deliver a true f/1.4, f/2, or whatever at infinity and get progressively "slower" at closer planes of focus. Similar problems occur with zooms at different focal lengths. These failings apply to both ways of setting the aperture opening. Does all this leave us in the weeds? Probably only if we are using an external meter or are a little al-retentive about rightness of settings. TTL metering provides compensation for attenuation due to focal length and/or extension for close focus. Also in our favor is that differences from the expected aperture diameter are usually quite minimal at all but the narrowest settings. If you have doubts and your lens has an aperture ring, you can do comparison shots of an evenly-lit blank wall for a given f-number. Steve Most aperture rings support at most 1/2 stop increments and often not for all stops. In a similar vein, if the camera is set to 1/3 stop increments and the aperture ring has no settings that correspond to a 1/3 stop, there is no point for comparison. ** Probably not a bad idea for a future feature. After all, we fine-tune AF, why not aperture control?

03-13-2019, 07:37 PM - 3 Likes	#7
dms Site Supporter Join Date: Aug 2011 Location: New York, NY Photos: Gallery Posts: 2,192	Originally posted by Adam The aperture ring is obsolete (on DSLRs). Unless you are reverse mounting the lens or something like that, then simply leave the aperture ring in the "A" setting and then set the aperture using the e-dial (or automatically). I respectfully disagree. It is sometimes very useful to set the exposure in M mode, and then depending on the subject/lighting very quickly change the aperture setting on the lens to adjust the exposure (and thus almost instantly get the shot). It requires you to have a reasonable sense of exposure/estimating the change needed, and comfort using the aperture ring--but these are likely normal for many of us--especially coming from the (slide) film era. Last edited by dms; 03-13-2019 at 07:52 PM. Reason: fix typo

03-14-2019, 03:11 AM - 2 Likes	#8
Paul the Sunman Pentaxian Join Date: Aug 2011 Location: Melbourne Photos: Gallery Posts: 4,843	Originally posted by Adam The aperture ring is obsolete (on DSLRs). The most recent Pentax lens release (HD FA 35mm f/2) has an aperture ring.

03-14-2019, 07:53 AM - 1 Like	#9
clackers Otis Memorial Pentaxian Join Date: Jul 2013 Location: Melbourne Photos: Albums Posts: 16,397	Originally posted by Paul the Sunman The most recent Pentax lens release (HD FA 35mm f/2) has an aperture ring. Very mischievous of you, Paul!

03-14-2019, 10:33 AM - 2 Likes	#10
Racer X 69 Moderator Man With A Camera Join Date: Jun 2010 Location: The Great Pacific Northwet, in the Land Between Canada and Mexico Photos: Gallery \| Albums Posts: 28,068	Bring back the aperture ring, and the A setting. I shoot nearly 100% in manual mode. I use the camera to meter the scene, except for night time and low light shots, which I usually guess at. Most of my lenses are manual lenses, and I have been leaning towards the ones with the A setting. I like the A setting, because I can set the aperture using the thumbwheel on the camera, and see what aperture I am at in the viewfinder. I prefer having the aperture ring so when I am using a bellows or extension tubes, or shooting with the lens reversed, i still have control over the aperture. I know, there is an adapter that adapts K mount lenses to Nikon, that has an aperture ring to manually control the aperture, and if one removes the optics it has to adjust for infinity focus when used as designed, it facilitates using lenses without aperture rings. sigh Guess I just am nostalgic about the aperture ring.

03-14-2019, 11:00 AM - 1 Like	#11
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Racer X 69 Guess I just am nostalgic about the aperture ring. Me too. I prefer the lens controls to be on the lens and the camera controls to be on the camera. With a non-crippled mount, this works very nicely, even on a "modern" camera (example: Pentax MZ-S) and if such a mount were on the K-3 successor, I would be the happiest of clams with the option of both e-dials and aperture ring. Steve

03-14-2019, 12:22 PM - 2 Likes	#12
Mikesul Loyal Site Supporter Join Date: Sep 2009 Location: Phoenix, AZ Posts: 7,594	There may be a trend in the industry. The recent, highly rated and very expensive Sony GM primes (24 1.4, 85 1.4 and 135 1.4) have aperture rings and, of course, the A position.

03-14-2019, 01:04 PM	#13
WPRESTO Loyal Site Supporter Join Date: Aug 2010 Location: Massachusetts Photos: Gallery \| Albums Posts: 59,107	I doubt that a manually set aperture set via an aperture ring is necessarily more accurate than one set using an "A" setting and letting the camera set the aperture, that is, if you set f5.6 on an aperture ring, it's unlikely it is more precisely and exactly f5.6 than the aperture the camera sets when using the "A" setting and selecting f5.6 via the camera. And if the lens is set to anything other than infinity, chances are the aperture won't be exactly f5.6 regardless of whether the lens is unit focusing or internal focusing. AND ALSO, the human eye can barely detect a 1/3 f-stop change, so if either the ring or the camera sets f5.6 within plus or minus about 20%, it's nearly certain that you could not tell the difference.

03-14-2019, 09:22 PM - 1 Like	#14
Posse96 New Member Join Date: Feb 2019 Location: San Francisco Posts: 6 Original Poster	Good Evening, I thank you all, fantastic feedback. Of course, I wake up in the middle of the night, starting to realize what you all conveyed. I have to shake my head at myself as I work in DNA Forensics and Biometrics. I can build a $5 Mln ABIS (Automated Biometric ID System), and yet, there are times when, as I noted, the obvious just escapes me. As most pointed out, I awake in bed; "you idiot, you're using the cam dial to set the settings" and it just went from there. I agree with those who highlighted variations in lenses and quality. I will say, I've been very pleased with the Pentax SMC 15mm f/4.0 DA ED AL Limited Wide Angle. Yet was so so with the Pentax DA 55-300mm f/405.8 ED lens. My goal now is to find a good landscape lens. I've been making the move back to prime lenses and find I wasn't satisfied with a large range zoom like the 55-300mm as photo clarity and quality didn't see that great. I accept all recommendations on suggestions for a solid landscape lens. Again, thanks everyone. I really appreciate the patience of a guy who, as I say; train went into the ravine (my explanation of a lost thought).

03-15-2019, 07:06 AM	#15
Racer X 69 Moderator Man With A Camera Join Date: Jun 2010 Location: The Great Pacific Northwet, in the Land Between Canada and Mexico Photos: Gallery \| Albums Posts: 28,068	Originally posted by Posse96 Good Evening, I thank you all, fantastic feedback. Of course, I wake up in the middle of the night, starting to realize what you all conveyed. I have to shake my head at myself as I work in DNA Forensics and Biometrics. I can build a $5 Mln ABIS (Automated Biometric ID System), and yet, there are times when, as I noted, the obvious just escapes me. As most pointed out, I awake in bed; "you idiot, you're using the cam dial to set the settings" and it just went from there. I agree with those who highlighted variations in lenses and quality. I will say, I've been very pleased with the Pentax SMC 15mm f/4.0 DA ED AL Limited Wide Angle. Yet was so so with the Pentax DA 55-300mm f/405.8 ED lens. My goal now is to find a good landscape lens. I've been making the move back to prime lenses and find I wasn't satisfied with a large range zoom like the 55-300mm as photo clarity and quality didn't see that great. I accept all recommendations on suggestions for a solid landscape lens. Again, thanks everyone. I really appreciate the patience of a guy who, as I say; train went into the ravine (my explanation of a lost thought). The Pentax A28mm (three different versions) should work well. I have the Sigma 28mm f2.8 Mini Wide and have used it quite a bit since I picked it up. There is an A version of this lens I would like to try.